Contactless power systems typically consist of a power transmitter that generates an alternating magnetic field and one or more power receivers coupled to the generated magnetic field to provide a local power supply. These contactless power receivers are within proximity, but electrically isolated from, the power transmitter. A contactless power receiver includes a power receiving coil in which current is induced by the magnetic field generated by the power transmitter, and supplies power to an electrical load.
Conventionally, power is transmitted directly to the receiver side load as soon as the transmitter and receiver sides are coupled. In the Applicant's U.S. Provisional Application No. 61/722,564 entitled “Inductively Coupled Power Transfer Method and Systems” filed Nov. 5, 2012 (now published as PCT Pamphlet No. 2014/070026 with an international filing date of Nov. 5, 2013), the entire contents of which are hereby incorporated by reference, description is made of a power transmitter which has a low power standby state: in which the transmitter is capable of detecting coupling of a power receiver; from which the transmitter wakes up or is “activated” only when such coupling is detected; and into which the transmitter enters when such coupling is ceased. Various detection circuitry and methods are described and generally involve the transmission of low energy pulses via the transmitter coil and detection of any change in electrical conditions within the transmitter side circuitry.
However, in many ICPT systems it would be further advantageous to ensure compatibility between the transmitter and receiver before power is delivered to the receiver side load.